The present embodiments relate to ordering and/or pairing of ribs. In particular, ribs represented in scan data are automatically labeled.
Ribs from medical scans of the chest are routinely viewed by radiologists. For example, computed tomography (CT) scans are used to view ribs for oncology evaluation or trauma reporting. Since ribs span through several axial image slices in oblique angles, the ribs may be difficult to view with a sufficient understanding of overall structure.
Computer aided automatic labeling of the ribs may be valuable to expedite reading and important in related applications, such as rib cage visualization, nodule registration, and pathology recording. Ribs serve as a frame of reference for intra/inter subject evaluations and facilitate registration across multiple scans for pulmonary nodule studies. The natural ordering and pairing of ribs are useful features in accurate localization and recording of lesions and pathologies of the lung. Correct labeling of the ribs may aid precise delineation of rib metastases and fracture locations.
The clavicles, xiphoid process, and sternal angle have been traditionally used as anatomic landmarks for rib counting in CT scans. Ribs are often ordered based on their relative spatial relationships and length ratios and labeled using their relative location with respect to the spine. In one approach, left and right side ribs are identified by comparing each rib centerline's centroid to the overall center of gravity of all the centerlines. Then, from each side, the closest centerlines above and below the longest centerline are found using the axial position of the constituting ridge voxels, repeating the scheme in tandem to obtain rib numbers. In another approach, the heuristic that the axial slices typically containing the apex of the lungs also contain the second pair of ribs is used. The second rib pair is identified from the segmented lung apex and the spine profile, following which other ribs are labeled sequentially while using the rib interval to identify possible missing ribs. In yet another approach, the first rib is identified as a sloping line that appears in a key sagittal plane image, and other ribs are detected as small ovals under the top rib.
These approaches may suffer from anatomic variability and fail under conditions such as scoliosis that alter the curvature of the spine, distorting the structural regularity of the rib cage. Ribs fractured due to trauma or pathology, missing ribs due to detection errors, or anatomically fused ribs may distort average rib intervals, resulting in problems with some of the approaches. Rib length ratios are not reliable for short ribs, such as the twelfth rib. The assumption about the second rib pair being closer to the apex of the lungs does not always hold true. In contrast enhanced CT images, often the contrast agent misleads detection of the top rib and subsequent ribs cannot be placed correctly. Many of the heuristics do not operate with abdominal and partial thoracic scans because of partial ribs and lack of sufficient spine context.